It is known in the art to produce multiple amplitude and phase modulated signals that can assume discrete states of a multi-state signal constellation. Quadrature Amplitude Modulation (QAM) is one such known technique. Prior devices which have produced such signals have employed the use of elements such as travelling wave tube amplifiers (hereinafter "TWTAs"). A problem may occur during use of TWTAs however, since in order to reduce constellation distortions in applications where constellations are complex and have many possible states (e.g., 64 QAM), TWTAs need to be operated in a high backoff, very linear operating mode. However, when operated in this mode TWTAs do not perform efficiently. Thus, the use of TWTAs is not optimum for applications wherein high operating power efficiency is required with complex QAM waveforms. One such application is a satellite-based transmitter of QAM signals.
In high rate data signal transmission applications, such as satellite applications, wherein it is necessary to transmit microwave signals through severely bandwidth-limited frequency channels, it is a desirable goal to efficiently transmit many data bits per state of a QAM signal constellation.